This invention relates to the casting of metal components and in particular to the manufacture of ceramic shell moulds.
Ceramic shell moulds are made by dipping a wax pattern of the component to be cast in a slurry consisting of a filler and a binder and stuccoing ceramic particles on the deposited slurry.
One of the prime considerations for a successful mould material is to achieve a co-efficient of thermal expansion close to that of the metal to be cast in order to minimise stress on the casting after solidification.
Prior known ceramic shell moulds are usually a compromise between suitable co-efficients of expansion and high temperature strength. The RR formulation shell mould material (PDS93) comprises a slurry of zirconium silicate particles in an alcohol based silica binder with a stucco material of tabular alumina particles. Whilst this material has relatively high thermal expansion characteristics for the casting of nickel super alloys it softens at high temperatures and tends to bulge under the metal pressure. Silica has a very low thermal expansion co-efficient and is very rigid and strong at high temperatures.